The research aim is to analyze and investigate the derminants and clinical significance of variations in population-based rates of coronary artery bypass surgery (CABS) among small geographic areas and subpopulations in Maryland. The research will address the important policy questions of whether high surgical rates imply lower standards of care, inappropriate surgery and greater risk to patients. It will also begin to address the question of whether low rates imply pockets of unmet medical need. The long-term objective is to contribute to an understanding of how population characteristics and physician practice style differences affect utilization rates, and to address the question of what are optimal rates from the perspective of improved health status. Using 1984-85 uniform discharge data from all Maryland acute care hospitals and 1980 Census data, CABS rates for defined geographic areas will be computed and correlated with the prevalence of coronary artery disease, race, income, education and insurance coverage. Direct and indirect age and sex-adjusted rates will be computed for each area, and for areas grouped by median family income+ educational level. Race-specific rates will be calculated as will rates for three insurance groups: Medicaid, Medicare and private. A multivariate regress using unit record and geographic variables will be carried out to determine the relative contribution of patient characteristics described above. Comparisons of patient risk factors (old age, comorbidity) and health outcomes (ALOS and peri-operative mortality) among high, medium, and low rate areas will be carried out. The research will try to determine whether physician standards of patient selection vary in relation to CABS rates. This will answer the question of whether high rates are associated with more inappropriate surgery. Chart reviews using pre-established criteria by an expert panel and a standard abstract form will be done to rate cases as inappropriate, based on their score. Differences in the proportion of inappropriate cases between high and low rate areas will be examined. A small sample of cases of Coronary angiography will also be reviewed to determine differences between cases of CABS and those not receiving surgery.